Acquired a powered wheelchair with charger. The charger seems to signal two
charged conditions: "Bulk charge complete", and "Charge complete". Charging
seems to progress from the former to the latter. What's the significance of
bulk charge?

The "bulk charge" is a high current charge to bring the battery back
from low levels, the the "charge complete" should occur after the
battery has had a higher voltage (than the bulk) applied to finish the
charging and enter "float" or terminate the process. There are many and
varied applications of that process.

Thanks for that. Seems to me that this complex charging method would
make sense if it incorporated some kind of monitoring of the battery
condition
as it progressed. But I disconnected the charger after the "Bulk charge
complete" indicator showed (after about four hours of charging),
and then re-connected later thinking the cycle would continue from there
to the "Charge complete" condition.
It didn't. It started all over, indicating "Bulk charge...." after another
four hours,
or so, suggesting that the charger was quite dumb and had assumed the
battery was
flat (which it certainly wasn't). Anyway, maybe I'm the dumb one and missing
something.

Bulk charge is typically a high constant current charge until the
battery reaches the cyclic voltage.
Absorption charge is holding the voltage at the cyclic voltage until the
current falls to a low level.
Finally the voltage is dropped back to the float voltage where it can be
held indefinately.

Putting battery back onto a charger if it is not fully charged usually
will start a bulk charge cycle until the cycliv voltage once again is
reached.